There is conventionally known an obstacle warning apparatus, which detects an obstacle existing around a vehicle and issues a warning that notifies a driver of an existence of the obstacle. For example, Patent literature 1 discloses an obstacle warning apparatus, which detects an obstacle with an obstacle sensor, records a relative position of the obstacle relative to a vehicle, and calculates a movement amount and a movement direction to update the recorded relative position of the obstacle when a position of the vehicle changes. A warning is issued when the distance between the vehicle and the relative position of the obstacle is equal to or less than a predetermined distance.
In addition, Patent literature 2 discloses an obstacle warning apparatus that issues a warning when there is a possibility that an obstacle detected by an obstacle sensor may be involved due to a turning radius difference between tracks followed by front and rear inner wheels when turning.